fac ‐[TcO 3 (tacn)] + : A Versatile Precursor for the Labelling of Pharmacophores, Amino Acids and Carbohydrates through a New Ligand‐Centred Labelling Strategy

Herein, we report a protocol for the synthesis of [ 99m TcO 3 (tacn)] + ([ 1 ] + ) (tacn=1,4,7‐triazacyclononane) that is suitable for clinical translation. Bioconjugates containing pharmacophores ([TcO(NO 2 ‐Imi)(tacn)] + ; [ 3 ] + ), artificial amino acids ([TcO(Fmoc‐allyl‐His)(tacn)] + ; [ 5 ] + ), and glucose derivatives ([TcO(allyl‐tetraacetylglucose)(tacn)] + ; [ 7 ] + ) were synthesized by cycloaddition strategies and fully characterized ( 99 Tc and 99m Tc). These new technetium complexes are stable at neutral pH and demonstrate the potential and flexibility of the [3+2] cycloaddition labelling concept. In addition to the synthetic work, the first biodistribution studies of [ 1 ] + and the small [3+2] cycloadduct [ 99m TcO(NO 2 ‐Imi)(tacn)] + ([ 3 ] + ) were completed. The biodistribution studies suggest the stability of these complexes in vivo. Furthermore, it was demonstrated that the high hydrophilicity of the [ 99m TcO 3 (tacn)] + building block is a complement to the complexes of the fac ‐{Tc(CO) 3 } + core.